The present disclosure relates to a communication device which communicates with the other communication devices by a communication method such as TCP (Transmission Control Protocol).
Currently, TCP is widely used in the internet, intranets, and the like. In the TCP, when a data reception side communication device receives a packet from a data transmission side communication device, the reception side communication device transmits an acknowledgement (ack) back to the transmission side communication device. Accordingly, in the TCP, it is possible to realize communication with high reliability.
In the TCP, a slide window manner is employed; the transmission side communication device sequentially transmits the packet to the reception side transmission device to slide a window when the acknowledgement (ack) arrives.
In the TCP, generally, a flow control and a congestion control are performed. In the flow control, the reception side communication device reports the latest window size to the transmission side communication device. The transmission side communication device transmits a packet of a transmission amount corresponding to the reported reception window size. Accordingly, it is possible to prevent the packet from overflowing from a reception buffer of the reception side communication device.
Meanwhile, in the congestion control, the transmission side communication device controls a congestion window size according to a slow start algorithm and a congestion avoidance algorithm to avoid the congestion of the network. In the slow start algorithm, the congestion window size is set to 1 MSS (Maximum Segment Size) for the first time, and the congestion window size gradually increases. In the congestion avoidance algorithm, a process of detecting the congestion from loss of the packet or change of RTT (Round Trip Time) and adjusting the congestion window size is performed. When the packet is transmitted from the transmission side communication device, the packet of the transmission amount corresponding to the smaller sized window of the congestion window size and the reception window is transmitted.
A technique related to the TCP is described as follows in Japanese Unexamined Patent Application Publication No. 2006-005833 and Japanese Unexamined Patent Application Publication No. 2006-279730.